Several tray designs are known for gas-liquid contactors used in processes including reactions and separations. In each design, trays are situated within the towers for contact between the components of mixtures within the towers. Several tray designs are known, as described by, for example, Philip C. Wankat in “Equilibrium Staged Separations” published by Elsevier (1988), C. Judson King in “Separation Processes” published by McGraw-Hill Book Company (2nd edition, 1980), and Henry Z. Kister in “Distillation Design” published by McGraw-Hill, Inc. (1992).
In a conventional tray design as illustrated, for example, by Kister in FIG. 7.7 on page of “Distillation Design” flow of liquid across a tray tends to follow the shortest path across the tray deck from the inlet downcomer toward the outlet downcomer. A consequence for chemical process towers having a circular cross-sectional design in which there are stagnant regions develop on the areas of the tray deck near the walls of the tower. The flow pattern is shown by King in FIGS. 12-15 and 12-16 on page 614 of “Separation Processes.” FIGS. 12-16 shows that there is non-uniform flow of liquid across a plate and, in extreme cases, recirculation cells are formed. This non-uniform liquid distribution also exists on conventional multi-pass trays where the downcomer bottom chord and outlet weir are always in different lengths.
It is desirable to effect good mixing of all components on the tray deck. When there is highly non-uniform liquid distribution above the tray arising from extensive back-mixing, the Peclet number approaches zero. When there is very little back-mixing i.e. uniform distribution of liquid across the tray, the Peclet number approaches infinity. The variation in Peclet number for diffusion liquid-mixing is illustrated by King in FIGS. 12-19 on page 619 of “Separation Processes.” For a given point efficiency, the Murphree efficiency of a tray increases as the Peclet number increases, and so it is desirable to maximize the Peclet number.
The tray deck is perforated to allow gas to rise through the perforations and bubble through the liquid flowing across the tray deck, thereby effecting contact between the liquid and the gas. An outlet weir is situated toward the edge of the tray deck adjacent the outlet downcomer, so as to maintain a depth of liquid and froth across the tray deck. Froth is formed when gas rises as bubbles through the liquid. It is important that the froth height is approximately even at all locations along the length of the outlet weir, as uneven froth height causes high entrainment and thus premature flooding.
What is needed is a tray designed to have higher capacity and efficiency in which the distance traveled by all liquid across the tray deck is essentially similar for all paths along which that liquid flows, so as to achieve:
a high Peclet number due to very little or no back-mixing, and so very uniform distribution of components in the mixture above the tray,
no stagnant regions above the tray decks, and
a froth height that is even across the length of the outlet downcomer weir.